Operation of an internal combustion engine is controlled by a plurality of actuators. With a spark ignition type internal combustion engine, the operation is controlled through an adjustment of an intake air amount by a throttle, an adjustment of ignition timing by an ignition device, and an adjustment of an air-fuel ratio by a fuel supply system. A control amount (or an operation amount) of each of the plurality of actuators may be determined for each individual actuator. Use of torque demand control as disclosed in JP-A-10-325348, however, allows torque control accuracy to be enhanced through coordinated control of the plurality of actuators.
The torque demand control is a type of feed-forward control that represents requirements relating to performance of the internal combustion engine by torque and controls operation of various actuators so as to achieve the torque requirements. To perform the torque demand control, a model for deriving a control amount of each actuator from the torque requirement, specifically, an inverse model of the internal combustion engine is required. The engine inverse model may be formed of a map, a function, or a combination thereof. JP-A-10-325348 discloses a technique that enables the torque demand control by using a common model (called control target amount calculation means in the Publication) during an idle state and a non-idle state of an internal combustion engine.